Skip including cpuid.h under Windows with Clang-cl

[ericstone93]

Summary

The issue is it includes <cpuid.h> when __clang__ is defined and __x86_64__ is set, but NOT on MinGW. This is the standard DirectXMath header from the Windows SDK.

On Linux/Mac with Clang, <cpuid.h> is a Clang/GCC built-in header that provides __cpuid and __cpuidex intrinsics. But on Windows with Clang-cl, those intrinsics come from <intrin.h> instead (which is already included on line 118 for _MSC_VER).

Since Clang-cl defines both __clang__ AND _MSC_VER, it hits both the <intrin.h> include (good) AND the <cpuid.h> include (bad, doesn't exist on Windows). The fix is to exclude _MSC_VER as in the PR.

Change

Add !defined(_MSC_VER) to the <cpuid.h> include condition so it only applies to non-MSVC-compatible Clang/GCC on Linux/Mac x86 targets.

[walbourn]

@Andrew-Farrier I recall we specifically used cpuid.h instead of intrin.h for DirectXMath 3.14. IIRC, the intrin.h approach resulted in bad codegen on clang for Windows.

Do you remember the bug? Any way we can verify if it's fixed in newer clang compilers (the issue dates back to the Windows SDK (19041) timeframe).

[walbourn]

The original issue was that __cpuid and __cpuidex signatures in clang/LLVM did not match MSVC. This appears to be fixed in modern clang/LLVM, but I'm trying to determine when. It looks like it may be that the change here would make the library lose compat with clang/LLVM v12 - v15, so I need to see if that's the case.

[walbourn]

Library still builds with clang-cl v12, so I'm going to go with this one.

That said, there are some additional files in the repo that need updating for this change as well:

Extensions\DirectXMathAVX.h
Extensions\DirectXMathAVX2.h
Extensions\DirectXMathBE.h
Extensions\DirectXMathF16C.h
Extensions\DirectXMathFMA3.h
Extensions\DirectXMathFMA4.h
Extensions\DirectXMathSSE3.h
Extensions\DirectXMathSSE4.h

[walbourn]

There are also some new warnings here that need a cast:

__cpuid(CPUInfo, 0x80000000);
__cpuid(CPUInfo, 0x80000001);

Both need to be:

__cpuid(CPUInfo, static_cast<int>(0x80000000));
__cpuid(CPUInfo, static_cast<int>(0x80000001));